The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the subject matter of the present disclosure.
A “data eye” is a plot formed when a digital signal from a receiver is repetitively sampled and the signal amplitude forms a vertical value, while the data rate—i.e., time—provides the horizontal value. For some types of signals, the pattern produced looks like a series of eyes. The eye pattern provides information on the state of the signal and the effects of channel noise and inter-symbol interference. A signal with good noise characteristics has a well-defined eye—empty space surrounded by a plurality of signal traces—while a noisy or otherwise low-quality signal has a poorly defined eye with signal traces impinging into what should be the empty space in the center.
In SerDes (serializer/deserializer) systems used for serial communication between and within integrated circuit devices, data eye monitoring (also known as “eye opening monitoring” or EOM) is used as a measure of signal quality or error rate. In a data path of an analog SerDes system, the analog data is sampled, and compared to a threshold to derive the data signals. The eye is monitored by replicating the sampling and thresholding (or “slicing”) circuitry in a parallel signal path and using that parallel signal path to sample data, sweeping through different sample points and different thresholds, other than or in addition to the sample points and thresholds used in the data path, to determine the form of the eye. An EOM error rate can then be determined by comparing the output of the parallel monitoring path to the output of the data path.
In a digital SerDes system, based on an analog-to-digital converter (ADC), EOM can be performed similarly to analog systems. Moreover, known digital EOM systems are frequently “destructive” (i.e., the monitoring affects the data signal) because normally less than the full signal path is replicated. Replicating the full digital receiver path for EOM, while non-destructive, has significant impacts on device area, power consumption and performance, because an ADC-based digital SerDes includes digital signal processing circuitry, including filters.